Outlook Attachment Size Limit: Max File Size (2026)
Outlook’s attachment cap depends on which version you’re using: Outlook.com (web) allows 34 MB of files from your computer, while desktop Outlook defaults to 20 MB — though Microsoft 365 and Exchange Online mailboxes generally raise that to around 150 MB. Here’s how it works.
The Limits at a Glance
Outlook.com (web)
- 34 MB combined for files attached from your computer
- Larger files: share via OneDrive instead
Outlook desktop (Exchange / Microsoft 365)
- Defaults to a 20 MB internet-email attachment limit
- Microsoft 365 / Exchange Online mailboxes generally allow up to ~150 MB (admin-configurable)
The Lower of Sender and Recipient Limits Applies
Attachment size isn’t decided by your side alone. Email passes through the recipient’s mail server too, and the lower of the sender’s and recipient’s limits wins. You might be able to send 100 MB, but if the recipient’s server rejects anything over 25 MB, the message bounces.
On desktop Outlook with a Microsoft 365 or Exchange Online mailbox, the default 20 MB internet-email limit can be raised by an admin up to roughly 150 MB. Outlook.com’s web limit is fixed at 34 MB for files attached from your computer.
How to Send Files Larger Than the Limit
- Attach as a OneDrive cloud link. Upload the file to OneDrive and use “Share link” so Outlook sends a link instead of the file itself — this is the standard fix for oversized attachments.
- Compress the files into a zip to get under the cap.
- Split a large file across multiple emails if compression isn’t enough.
- Check the recipient’s limit if a message bounces — their server may reject what yours allows.
Troubleshooting
What’s the maximum attachment size in Outlook?
34 MB on Outlook.com (web). Desktop Outlook defaults to 20 MB, but Microsoft 365/Exchange mailboxes often allow up to ~150 MB (admin-set).
Why does my Outlook attachment fail to send even though it’s under my limit?
The recipient’s server may have a lower limit. The smaller of the two limits applies.
How do I send a file that’s too big to attach?
Upload it to OneDrive and insert a “Share link” instead of attaching the file directly.
Can an admin change the desktop attachment limit?
Yes. On Microsoft 365/Exchange Online, the attachment size limit is admin-configurable up to about 150 MB.
Quick Reference
| Version / mailbox | Limit |
|---|---|
| Outlook.com (web) | 34 MB combined |
| Outlook desktop, default | 20 MB |
| Microsoft 365 / Exchange Online | Up to ~150 MB (admin-set) |
| OneDrive share link | Far larger files |
If filing and sending attachments slows you down, an AI assistant like Carly can handle it from your inbox — see the best AI email assistants and the best email management tools.
Related guides: Best AI Email Assistants · Best Email Management Tools · Best AI Assistants for Outlook
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